How to Use a Snellen

The Snellen eye chart was first invented by Dr. Hermann Snellen in 1862. Today, the chart is used by ophthalmologists, optometrists and driver examination centers to test a person's visual acuity, which is the sharpness of eyesight. The eye doctor then measures the results of the tests and determines whether the subject needs glasses. The Snellen eye chart can be used at home to measure visual acuity.

Things You'll Need

• Measuring tape
• Masking tape

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Instructions

• 1

  Hang the Snellen eye chart onto the wall. The space used to administer the test should be well lit, and the eye chart should be placed at a height that is comfortable for the reader.

• 2

  Measure 20 feet back from the chart. Mark this point on the floor with a piece of masking tape. This is the standard distance that eye doctors use to measure visual acuity with a Snellen chart.

• 3

  Stand with your toes touching the line and place your hand over your right eye. Read each line of the chart, beginning with the top line. Continue to read each descending line until you are no longer able to clearly make out all of the letters. Have a friend or family member there to assist you by writing down the number adjacent to the line and to verify that you have correctly read all of the letters. For instance, the number "40" would be written down if you could successfully read all of the letters on the fifth line of the test.

• 4

  Repeat this process with your left eye covered. Once again, make a note of the last line in which you could successfully read all of the letters.

• 5

  Interpret the results. For instance, if you could read the line labeled "40," you have 20/40 vision. This means that you can read letters from 20 feet away that a person with normal vision could read from 40 feet away.